Fluid probe

ABSTRACT

A device for detecting a property of a fluid includes a body region and a flexible element having a first end and a second end. The first end is fixedly located on the body region. The flexible element is arranged to move from at least a first configuration to a second configuration via bending of the flexible element. The flexible element includes an actuating portion arranged to move the flexible element between the first configuration and the second configuration. The device also includes a movement detector for detecting movement of the flexible element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/596,208, filed Jun. 2, 2006, which is the national stage ofInternational Patent Application PCT/GB2004/005079, filed Dec. 3, 2004(which was published in English), which claims the benefit of priorityto British Patent Application No. 0328054.2, filed Dec. 4, 2003.

This invention relates to the determination of properties of fluids, andin particular is suitable for, although not restricted to, thedetermination of the viscosity of fluids such as blood.

Determining the properties of a fluid is crucial in a wide range ofindustries. For example it is important to know the viscosity of oil inthe oil industry and the temperature of milk in a dairy. Measurementscan be taken continuously in real time, or at specific times, eitherwith an appropriate ‘in-situ’ sensor, or by placing an appropriatesensor into the fluid of interest and then taking a reading.

An important property of many fluids is its viscosity. For example, theviscosity of the blood is crucial to the determination of the bloodpressure of the patient. Furthermore, by continuous monitoring of ablood sample, the rate of clotting can be determined. The clotting rateof a patient's blood can be used to diagnose certain conditions, such asdeep vein thrombosis.

Current devices used for measuring viscosity (‘viscometers’ or“viscosimeters”) have a number of disadvantages. The devices aregenerally large, bulky and expensive to both purchase and manufacture.

If a fluid sample is valuable, for example economically (a new medicine)or otherwise (the blood of a patient), it is undesirable to use andpossibly waste large amounts of that sample in determining itsproperties. Due to the large size of state of the art viscometers, acorrespondingly large fluid sample has to be utilised. Furthermore, itis often necessary to take a sample from its local environment in orderto undertake a measurement. In doing so, stabilising agents often haveto be added to the sample so as to prevent the measurements of thesample being adversely affected during transport from the sampling siteto the viscometer. For example, coagulants are added to blood whenretrieved from a patient so as to prevent the blood from clotting whenexposed to air. Any addition of such an agent contaminates or reducesthe purity of the sample, often affecting its properties and is thusundesirable. Ideally, measurements should be taken either in-situ, orwithout the need for addition of agents.

According to a first aspect of the present invention, there is provideda method of determining a property of a fluid using a sensing elementcomprising a flexible element movable from a first configuration to asecond configuration via bending of the flexible element, the flexibleelement comprising an actuating portion arranged to move the flexibleelement between the first configuration and the second configuration,the method comprising inducing movement in the flexible element betweenthe first configuration and the second configuration by applying a heatsignal to the flexible element, receiving a signal from the sensingelement, the signal being indicative of movement of the flexible elementwithin the fluid and processing the signal to determine a valueindicative of at least one property of the fluid.

The inventors have realised that such a method can be used to measurethe viscosity, shear, flow rate or temperature of a fluid simply byusing a heat signal to move the flexible element. Furthermore, thesensing element can be constructed so as to be of dimensions of theorder of micrometers. Hence, in-situ or on location measurements can bemade of extremely small samples, negating the need for addition ofstabilising agents.

Most preferably, the signal is processed to determine a value indicativeof at least one property of a group comprising viscosity, temperature,flow rate and shear rate.

The method may further comprise determining a rate of change of movementof the flexible element, by monitoring a change in the received signalwith time and determining a value indicative of the viscosity of thefluid from the rate of change of movement.

The method may further comprise determining an amplitude of movement ofthe flexible element from the received signal for a given applied heatsignal and determining a value indicative of the viscosity of the fluidfrom the amplitude.

The method may further comprise the step of determining the resonantfrequency of the flexible element in the fluid by applying a pluralityof different frequency heat signals to the sensing element, monitoringthe amplitude of movement of the flexible element from the receivedsignal to identify a resonant frequency of the flexible element anddetermining a value indicative of the viscosity of the fluid from theidentified resonant frequency.

The method may further comprise determining a change in the movement ofthe flexible element and determining a value indicative of a flow rateof the fluid from the change in movement, the change in movement beingdue to flow of the fluid against the flexible element.

The method may further comprise determining a value indicative of ashear rate of the fluid by determination of the flow rate at a pluralityof locations within the fluid.

The actuating portion of the flexible element may comprise a laminate ofat least two layers, each layer having a different coefficient ofthermal expansion, and wherein the method may then further comprise,prior to induction of movement by application of the heat signal,determining a value indicative of the temperature of the fluid.

The device may comprise a plurality of flexible elements, and the methodmay further comprise using the plurality of flexible elements todetermine a value indicative of at least one property of the fluid in aplurality of locations.

The device may comprise a plurality of flexible elements, and the methodmay further comprise using at least one of the plurality to cause a flowwithin the fluid, and using at least one of the plurality to determine avalue indicative of at least one property of said fluid.

The method may further comprise holding the flexible element in at leastone of said two configurations by a magnetic force. Alternatively, themethod may further comprise holding the flexible element in at least oneof said two configurations by an electrostatic force.

According to a second aspect of the present invention, there is provideda device for detecting a property of a fluid comprising a body region, aflexible element having a first end and a second end, the first endbeing fixedly located on the body region, the flexible element beingarranged to move from at least a first configuration to a secondconfiguration via bending of the flexible element, the flexible elementcomprising a laminate of at least two layers and an actuating portionarranged to move the flexible element between the first configurationand the second configuration, the actuating portion being provided by atleast a first layer of the laminate having a different coefficient ofthermal expansion from a second layer of the laminate such that a changein temperature of the flexible element moves the flexible element fromthe first configuration to the second configuration, the flexibleelement further comprising a heating element for heating at least theflexible element thereby providing the change in temperature, and amovement detector arranged to detect the movement of the flexibleelement, and to provide a signal indicative of a property of a fluid inwhich the flexible element is immersed.

Preferably, the movement detector is arranged such that an electricalproperty of the movement detector changes due to movement of theflexible element. Most preferably, the movement detector comprises apiezoresistive element located on the flexible element arranged suchthat the electrical resistance of the piezoresistive element changes dueto movement of the flexible element.

The movement detector may comprise a capacitor having two plates, theflexible element forming one plate thereof, and an electricallyconducting plate forming the other plate, such that the capacitance ofthe capacitor changes due to movement of the flexible element.

The device may comprise latching means arranged to hold the flexibleelement in at least one of the two configurations.

The movement detector may comprise an electromagnetic radiation sourcearranged to direct radiation towards the element, and an electromagneticradiation detector arranged to detect electromagnetic radiation at leastone of: reflected from, transmitted through, refracted from ordiffracted by the flexible element.

Most preferably, the first layer of the laminate comprises a polymer.The first layer of the laminate may comprise a material selected from agroup consisting of polyimides, polyamides and acrylic polymers. Thesecond layer may comprise a polymer. The second layer may comprise amaterial selected from a group consisting of polyimides, polyamides andacrylic polymers.

Most preferably, the second layer of the laminate comprises a metal. Themetal may be selected from a group consisting of gold or aluminium.

Preferably, the length of the flexible element from the first to thesecond end is between 100 μm and 1 mm, and the distance between thesecond end of the flexible element in said first configuration and thesecond end of the flexible element in said second configuration isbetween 30 μm and 650 μm.

The device may comprise a plurality of flexible elements. Preferably,the plurality of flexible elements are arranged in a first row and asecond row, each row comprising at least one flexible element, theflexible elements being arranged such that the at least one flexibleelement of the first row extends in opposition to the at least oneflexible element of second row. Most preferably, the plurality of theflexible elements are interdigitated.

Embodiments of the invention will now be described by way of examplewith reference to the accompanying figures in which:

FIG. 1 is a perspective view of a detection device in accordance with apreferred embodiment of the invention;

FIG. 2 is a circuit diagram of a Wheatstone bridge circuit forming partof the device shown in FIG. 1;

FIG. 3 is a simplified perspective view of the detecting device of FIG.1;

FIG. 4 is a graphical representation relating an input signal to adetecting device to the change in resistance of a constituentpiezoresistive element;

FIG. 5 is a perspective view of a detecting device in accordance withanother embodiment;

FIG. 6 is a perspective view of a detecting device in accordance with afurther embodiment; and

FIG. 7 is a perspective view of a detecting device in accordance withyet another embodiment.

Illustrated in FIG. 1 is a perspective view of a detection device 1according to a preferred embodiment of the present invention. Thedetection device 1 comprises a body region 2, a flexible element 3, aheater 4 and a Wheatstone bridge circuit 5.

The flexible element 3 is an integral part of and extends from the bodyregion 2. The first end of the flexible element is connected to the bodyregion. The second end of the flexible element, distance from the first,is free to move in relation to the body region. The flexible element isa bar with a rectangular surface area, with the longer side of therectangle extending from the body region. The flexible element 3comprises a laminate of two layers 3 a, 3 b, the materials of each layerhaving different coefficients of thermal expansion. The materials can bedifferent materials, or the same material processed (e.g. stressed) soas to have different coefficients of thermal expansion.

Under application of heat, one layer will expand more than the other forthe same rise in temperature, and hence the flexible element 3 will bendin the direction of the material with the lower coefficient of thermalexpansion. Upon cooling, one layer will contract faster than another forthe same decrease in temperature, and hence the flexible element 3 willthen bend in the direction of the material with the greater coefficientof thermal expansion.

The heater 4 is located on the flexible element 3, and comprisesconductive material forming a continuous line or track 4 a across anarea of the upper surface of the flexible element 3. The heater 4further comprises electrical contacts 4 b for delivery of current to(and resulting in heat dissipation from) the heater 4. These electricalcontacts 4 b are located on an upper surface of the body region 2.

Wheatstone bridge circuits 5 are well known in the art as beingparticularly sensitive apparatus for the measurement of capacitance andresistance. A Wheatstone bridge circuit 5 is located on the body region2 and flexible element 3. The Wheatstone bridge 5 comprises four ‘legs’or ‘arms’ 5 a, 5 b, 5 c, 5 d, three of which 5 b, 5 c, 5 d, reside onthe body region 2, and one of which 5 a resides on the flexible element3 immediately adjacent the body region 2. The three legs 5 b, 5 c, 5 dresiding on the body region 2 each comprise a resistance of a knownvalue. The fourth leg 5 a, residing on the flexible element 3, comprisesa piezoresistive element 5 a. A piezoresistive material is one whoseelectrical resistance changes upon the application thereon of mechanicalstrain. Furthermore, the Wheatstone bridge circuit 5 compriseselectrical contacts 5 e, 5 f on an upper surface of the body region 2for input and output of electrical signals. The Wheatstone bridgecircuit 5 is illustrated in FIG. 2.

In use, a voltage is applied across the Wheatstone bridge circuit 5 viacontacts 5 e, and a voltage output is measured across the middle fromcontacts 5 f. When the output of the bridge 5 is zero, the bridge 5 issaid to be balanced and the resistances equal. When the resistance ofone of the legs 5 a, 5 b, 5 c, 5 d, changes, the previously balancedbridge 5 is now unbalanced. This unbalance causes a voltage to appearacross the middle of the bridge 5. From this value, the change inresistance can be calculated. However, the bridge 5 need not be balancedinitially. Although the initial output voltage may then be non-zero inmagnitude, the non-zero value can be used as a relative zero value. Theonly substantial variation in resistance of the Wheatstone bridge 5 willarise from the piezoresistive element, thus it can be assumed that anysubstantial variation in voltage output is attributed to the movement ofthe flexible element 3. Preferably the three known resistances areidentical and in close proximity to compensate for any temperaturevariations etc.

Surface micro machining of thin films can be used to construct thedevice shown in FIG. 1. In a preferred embodiment, polyimide and goldfilms are used to produce the flexible element 3. Polyimide (DuPont,Pyralene PI2566) is chosen for its high coefficient of thermal expansion(60×10⁻⁶ K⁻¹) and small Young's modulus (1.75 GPa), allowing largedisplacements with small change in temperature. Also, polyimide filmscan be easily spin-coated from the liquid phase allowing a range ofthickness to be tested for optimum deflection. Many other plasticpolymers can be used, also spin coated in their liquid phase, such asPI2722, PI2723 (both of which have a coefficient of thermal expansion of57×10⁻⁶ K⁻¹) or PI2734 (coefficient of thermal expansion of 13×10⁻⁶K⁻¹). Gold was chosen because of its appropriate mechanical and thermalproperties with respect to the PI2566 polyimide. For example, gold has aconsiderably lower coefficient of thermal expansion (14×10⁻⁶ K⁻¹) thanPI2566. The materials of each layer of the flexible element 3 are chosensuch that the distance moved by the flexible element 3 when heated isrelatively large, e.g. it may be of similar dimensions to the size ofthe flexible element. For example, for a flexible element 3 ofdimensions of the order of microns, materials are chosen such that themovement of the flexible element 3 is also of the order of microns.Polymers and/or metals can be used as the materials for the constituentlayers of the flexible element 3.

A method based on controlled delamination of thin films from a substratethrough forced variation is employed. This approach eliminates the needto protect layers from chemical degradation during a final etch releasestep and also allows freeing of arbitrary large areas.

The delamination technique is based on optical lithography and exploitsthe weak adhesion of gold to silicon, silicon dioxide or glass. Byinducing stresses in constituent layers of the flexible element 3, thenreleasing it from an anchoring layer on substrate 2, it may curl at anon-fixed end, extending from the body region 2. Any of the threematerials (silicon, silicon dioxide or glass) may be successfully usedas the substrate 2, which (substantially) forms the body region 2.

A thin layer of Cr, Ni or N—Cr (500 Å) 2 a is plasma sputtered onto thesubstrate 2 and acts as a first adhesion promoter between the substrate2 and subsequently plasma sputtered gold barrier layer 2 b (1000 Å). Thegold barrier layer 2 b is deposited to prevent oxidation of the adhesionpromoter 2 a upon exposure to air. The first adhesion promoter layer 2 aand gold barrier layer 2 b are then patterned to define the area fromwhere the flexible element 3 will be released i.e. parts of the firstadhesion promoter layer 2 a are removed. Patterning is done usingstandard lithography and wet etching techniques, obtaining openings inthe first adhesion promoter layer 2 a for the later forced delaminationof the flexible element 3. The pattern is essentially the inverse of theanchoring layer image i.e. material deposited above the region enclosedby the open ended rectangular structure will eventually form theflexible element 3, whereas material deposited about this region willform the anchoring layer from which the flexible element 3 will bereleased. The pattern is a thin track defining three sides of arectangle of dimensions 500 μm by 80 μm, and thereby an ‘open ended’rectangular structure. This effectively defines the size of the flexibleelement 3, which is also 500 μm by 80 μm. In being open ended, uponrelease, one end of the flexible element 3 remains fixed to the bodyregion 2, while another is free to move, extending from the body region2.

A gold structural layer (1.2 μm thick) 2 c, 3 a is then plasma sputteredon top of the patterned gold barrier layer (1000 Å). The gold structurallayer acts only as a passive mechanical layer and is electricallyinsulated from a heater 4 by a polyimide layer 2 d, 3 b whose depositionis described herein below. In the same deposition run, a thin Cr layer(not shown) (<500 Å) is deposited over the gold structural layer to actas an adhesion promoter for a subsequent polyimide layer.

A polyimide layer of PI2566 2 d, 3 b is then spin coated over the goldstructural layer 2 c, 3 a from the liquid phase and soft baked at 120°C. in an oven for 20 minutes. Thereafter, a 1500 Å thick Ni—Cr layer issputter coated and patterned to form the heater tracks 4 a, contact pads4 b and signal lines. Standard photolithography was carried out usingpositive tone photoresist to pattern the flexible element 3 and definecontact pads. Patterning was done using wet chemical etching. However,an alternative technique would be reactive ion etching (RIE) of thepolyimide layer. This would require a Cr layer to act as hard mask.Using similar techniques, a resistive Wheatstone bridge circuit 5 isalso deposited, including a constituent piezoresistive element 5 a andcontact pads 5 e, 5 f.

Finally, following the final depositions, a wet Au etch is performed torelease the flexible element 3 from the anchoring layer. Due to theinitial stresses in the constituent layers of the flexible element 3,there is no need for special release recipes. The induced force preventsthe flexible element 3 from sticking to the substrate 2. Thus, uponrelease, the flexible element 3 bends up and away from the body region1.

The thickness of the gold structural layer 2 c, 3 a of the flexibleelement 3 (1.2 μm) was chosen to offer good actuation results. The valueof 1.2 μm was empirically established. It was also established that forthe mechanical properties of the constituent materials of the flexibleelement 3 (Gold, PI2566), a thickness ratio of 4:1 produced the greatestinitial deflections, whereas a thickness ratio of 8:1 gave optimumexperimental results. It will be appreciated that other thicknesses andratios thereof could be employed. Also, thickness variation of thepolyimide layer 2 d, 3 b can be achieved by varying the spin speedduring spin coating. It will be appreciated that a second layer ofPI2566 could be spin coated to embed the heater 4 structure for improvedthermal insulation and also mechanical protection.

It will be appreciated that stress within constituent layers may besufficient to cause, upon release, the flexible element 3 to bend somuch that it curls back on itself, forming a ‘roll’ of material. Mostpreferably fabrication of the detecting device 1 is such that thissituation is avoided, such that upon release, the flexible element 3does not form such a roll. Preferably, the coefficients of thermalexpansion of the constituent layers 3 a, 3 b of the flexible element 3are different along the length of the flexible element 3 (defined by thedistance from the point at which the flexible element 3 is fixed to thepoint at which it is free), but the same along the width of the element,such that the flexible element 3 bends along its length, but does notbend substantially across its width.

For ease of description, use of the detecting device 1 is now describedwherein the flexible element 3 is flat and unbent. Parts of the bodyregion 2 not attached to and surrounding the flexible element 3 are nolonger illustrated so as to highlight the flexible element 3.Additionally, FIGS. 3 to 5 are less detailed than FIG. 1, in so far asthey do not illustrate constituent layers of the device 1. Similar partsare given the same reference numerals in each Figure.

When a current is made to pass though the track 4 a of the heater 4shown in FIG. 1, via the application of a potential difference acrossthe heater contacts 4 b, heat is dissipated due to electrical resistancein the track 4 a. This heat causes the temperature of the flexibleelement 3 to increase. In heating the flexible element 3, one layer ofthe laminate 3 b will expand at a greater rate than the other 3 a due tothe differential in their respective coefficients of thermal expansion.Hence, as illustrated in FIG. 3, the flexible element 3 will bend andbecome straighter—the flexible element 3 has been made to move from afirst to a second configuration. The end of the flexible element 3 ofthis embodiment can move through a distance in the range 200 μm to 250μm. In bending, the flexible element 3 induces a strain on thepiezoresistive element 5 a that will induce a change in its electricalresistance. Hence, in conjunction with the piezoresistive element, theWheatstone bridge 5 can be used as a strain gauge, the output voltage ofthe Wheatstone bridge circuit 5 reflecting the (change in) electricalresistance of (and strain upon) of the piezoresistive element 5 a.

For a given input signal to the heater 4 (a heat signal), the flexibleelement 3 will move (or ‘deflect’) a certain amount. If the heat signalis repetitive, varying from a ‘current on’ to a ‘current low’ or even‘current zero’ value, the flexible element 3 will continue to bend whenit is heated, and will relax towards its equilibrium position when no(or less) heat is applied to it, accordingly. The flexible element 3will effectively oscillate. If a damping force is applied that opposesthe movement of the flexible element 3, it will take longer to reachonly maximum possible deflection for a given input. Further, if the heatsignal is pulsed, the element may not reach this maximum deflection, asthe element is bent in the other direction due to the change in heatsignal. These effects can be used to detect and determine the viscosityof a fluid.

A more viscous fluid will have a greater damping effect on the movementof the flexible element 3 than a less viscous one. The change indeflection corresponds to a change in strain on the piezoresistiveelement 5 a, which in turn alters it resistance. As the piezoresistiveelement 5 a is a leg of a Wheatstone bridge 5, the change is reflectedin a change of output voltage of the Wheatstone bridge 5. Thus, from theoutput of the Wheatstone bridge 5, the change in deflection can bedirectly measured, and this corresponds to a change in the viscosity ofthe fluid. FIG. 4 illustrates the effect of damping on the movement ofthe flexible element 3.

FIG. 4 has two graphs, one illustrating the current supplied to theheater 4 and a corresponding graph displaying the corresponding absolutechange in the resistance of the piezoresistive element 5 a in fluids ofdifferent viscosities 7, 8. A square wave signal 6 is applied to theheater 4, and therefore heat to the flexible element 3. The applicationof heat induces movement of the flexible element 3, which in turn causesa strain to be induced in the piezoresistive element 5 a. Consequently,the resistance of the piezoresistive element 5 a will change 7 withmovement of the flexible element, which is directly related to theapplication of heat from the heater 4. By locating the flexible element3 in a more viscous fluid, the movement of the flexible element 3 willbe damped. The resistance of the flexible element 3 will change lessrapidly in a more viscous fluid 8. Further, in the example shown, theamplitude of resistance is less in the more viscous fluid 8. The changein resistance can thus be used to determine a change in the viscosity ofa fluid.

The resistance at the end of the signal pulse can be used to determinethe maximum deflection, this maximum changing for fluids of differentviscosities. However, it may be the case that the pulse duration(current ‘on’ time) is too great for the change in deflection to beresolved i.e. the flexible element 3 has the same maximum deflection inliquids of different viscosities for an identical input signal. This canbe accounted for by varying the length of time for which current isapplied to the heater 4 (and hence heat to the flexible element 3),and/or the magnitude of the current, and/or the period betweensuccessive current pulses. In short, the input signal can be tailored tothe situation as appropriate.

Alternatively, the resistance of the piezoresistive element 5 a ismonitored continuously such that its change with respect to time can beobserved. Hence, even if the resistance at the end of a pulse (i.e. thedeflection of the flexible element 3) is the same, the rate of change ofresistance will be different for fluids of different viscosities. Theresistance of the piezoresistive element 5 a will change more rapidlyfor a fluid of one viscosity than for a fluid with a second, higherviscosity. This is simply a consequence of the fact that, with aconstant driving force, a body's movement is quicker through a lessviscous liquid than for a fluid of a higher viscosity. Most preferably,the input signal is such that when no current is applied, the flexibleelement 3 is allowed to return to its equilibrium position i.e.dissipate all heat energy provided by the heater 4. Preferably, when nocurrent is supplied to the heater 4, the heater 4 supplies no heat tothe flexible element 3 i.e. the heater 4 dissipates heat extremelyquickly. If the flexible element 3 is made to oscillate, preferably thefrequency of the input signal is optimised to the dimensions of theflexible element. A high sampling rate (and hence high frequencyoscillation) may be required for some applications. It will be readilyappreciated that the same results can be achieved from a single inputpulse, causing a single deflection of the flexible element 3, for eachexperiment.

As well as using the change in resistance/deflection to measure theviscosity of a fluid, the resonant frequency of the flexible element 3can also be utilised for the same purpose. A resonant system is one inwhich a large oscillation is produced by a small stimulus ofapproximately the same frequency. The frequency at which this occurs fora given system is dependant upon the viscosity of the medium in whichthe oscillating part of the system is immersed. Thus, the flexibleelement 3 of the detecting device 1 will have an intrinsic resonantfrequency unique to the fluid in which it is immersed. Thus, by varyingthe driving frequency (the input signal to the heater 4) of the flexibleelement 3, while simultaneously monitoring the resistance of thepiezoelectric element 5 a (and thus deflection of the flexible element3), the amplitude of deflection of the flexible element 3 can bedirectly related to its driving frequency. Thus, the resonant frequencyof the flexible element 3 can be readily identified, and the viscosityof the fluid derived therefrom.

With its strain and temperature sensitivity, it is clear to see thatsuch a detecting device 1 has many applications other than themeasurement of viscosity. For example, the device 1 can be used tomeasure temperature, flow rate and shear of a fluid.

As with the application of heat from the heater 4, environmental heatwill cause the constituent layers of the flexible element 3 toexpand/contract accordingly. This expansion/contraction induces a changein the strain on the piezoresistive element which is detectable from theoutput of the Wheatstone bridge circuit 5 of which it is a crucial part.Thus, monitoring the initial position of the flexible element 3, priorto it being driven by a heat signal from the heater 4, can be used todetermine the temperature of the fluid.

It has already been described how the Wheatstone bridge circuit 5effectively operates as a strain gauge, using the piezoresistiveelement's 5 a inherent properties to achieve such functionality. If theflexible element 5 a is placed in a flowing fluid a change in magnitudeof the deflection of the flexible element 3 can be used to determine theflow rate of that fluid. The faster the flow of the fluid, the moreconstituent material per unit time is incident upon the flexible element3 and thus the greater the force upon the flexible element 3. A greaterforce on the flexible element 3 results in a change in magnitude ofdeflection, for a given applied heat signal.

The properties of a fluid sample can be determined in a plurality oflocations, thus determining a profile of said sample with respect tosaid property. For example, by measuring the flow rate of a fluid sampleat a number of locations, a flow rate profile, and thus the shear rate,can be determined. One such way of achieving a profile is to use asingle device 1 and move it through the sample, taking measurements atdesired locations. However, this leaves the possibility that a propertyat a specific location may change between successive measurements, thusgiving an inaccurate profile i.e. the property at the first location maychange by the time a measurement at another location is made. Ideally,the measurements can be simultaneously taken at the desired number oflocations. Preferably the measurements can be taken in real time. Realtime measurement may yield further fluid sample information, such as theclotting time of blood. By using a plurality of detecting devices 1,preferably one for each desired measurement location, such real time,multi-location measurement and thus profiling can be achieved.

It is clear that use of such a detecting device 1 will yield onlyrelative values of viscosity, temperature, etc. For example, anoscillating flexible element 3 will deflect substantially less in motoroil than in air. To obtain absolute values, calibration of the detectingdevice 1 and modelling of the fluid and/or flexible element 3 of thedetecting device 1 may be required. For example, deflection of theflexible element 3 for a given input signal may be measured in one ormore fluids of known viscosities, and from that, a specific change indeflection can be related to a specific change in viscosity. It willalso be appreciated that accurate modelling of the flexible element 3and its movement can yield properties about a fluid in which it isimmersed. It will also be appreciated that there are a variety ofinterdependent factors that may have a measurable effect on a givenmeasurement. For example, in heating the flexible element 3 to inducemovement therein, some heat energy will undoubtedly be transferred tothe fluid in which the device 1 is immersed. Such heat dissipation willraise the temperature of the fluid and may alter its viscosity, therebygiving a false measurement thereof. Similarly, the electrical resistanceof the piezoresistive element 5 a will change with temperature, thetemperature itself being related to the temperature of the fluid plusany effects due to the heater 4. All of these problems may be overcomevia a combination of calibration and/or modelling of the elementsnecessary to perform a desired measurement.

In another embodiment (not shown), the device 1 is generally similar tothat described in relation to FIGS. 1 and 2. However, in this embodimentthe Wheatstone bridge 5 now comprises capacitive elements as opposed toresistive elements, and the piezoresistive element has been removed.Instead, a conductive plate is located above, but not in contact with,the flexible element 3. Whereas in the device 1 of FIG. 1 a changingoutput signal resulted from a strain on, and corresponding change inelectrical resistance of, a piezoresistive element, in this embodiment,changes in capacitance are used to detect movement of the flexibleelement 3. The Wheatstone bridge 5 comprises a known capacitance on eachof three of its arms, and the conductive plate and flexible element 3form the plates of a fourth (variable capacitance) capacitor. If theflexible element 3 moves, the separation between it and the conductiveplate above will change and, from basic electrostatic theory, so willthe capacitance of this fourth capacitor. This detector device 1operates in an otherwise identical manner to, and has the functionalityof, the detector device 1 of FIGS. 1 and 2.

It will be clear to one skilled in the art that all of theaforementioned embodiments are not restrictive in any way, and are givenby way of example only. For example, all embodiments of the inventiondescribed thus far comprise a Wheatstone bridge 5 having four legs 5 a,5 b, 5 c, 5 d, three of which 5 b, 5 c, 5 d each comprise a constant andknown value of resistance/capacitance. The fourth leg 5 a comprises avariable resistance/capacitance sensitive to movement of the flexibleelement 3. By incorporating more movement sensitiveresistances/capacitances in other legs of the Wheatstone bridge 5 (i.e.replacing the known and constant value components) the sensitivity ofthe bridge may be increased. The sensitivity of the Wheatstone bridge 5is defined by the change in its output voltage for a small change in itsinput parameters i.e. variable resistance. If the output voltage can bemade to be greater for the same or smaller change in its inputparameters, its sensitivity is said to have increased. In comparisonwith the use of one leg, the use of two legs yields a two-fold increasein sensitivity, three legs a three-fold increase and four legs afour-fold increase. The incorporation of such additional movementsensitive resistances/capacitances can be achieved in a number of ways.

Taking a detecting device 1 incorporating a piezoresistive element forexample, two legs of a Wheatstone bridge 5 may each comprise apiezoresistive element. The piezoresistive elements of two adjacentflexible elements may form two of the legs of the Wheatstone bridge.Alternatively, using only a single flexible element 3, anotherpiezoresistive element (in addition to that residing on the flexibleelement 3 immediately adjacent the body region 2) may reside on theflexible element 3. By forming a Wheatstone bridge 5 utilising eachpiezoresistive element as a leg of the bridge, a more sensitive straingauge is created. For example, an additional piezoresistive element mayreside on the upper surface of the flexible element 3 at a point remotefrom the body region 2.

It will be appreciated that the piezoresistive element 5 a may resideanywhere on the flexible element 3, so long as the strain that is underchanges when the flexible element 3 moves. For example, thepiezoresistive element 5 a may be underneath the flexible element 3. Thepiezoresistive element 5 a may reside on the flexible element 3 adjacentthe body region 2 of the detecting device 1, at a point remote from thebody region 2 or at a point somewhere in-between these extremes. Thepiezoresistive element 5 a may reside on both the body region 2 and theflexible element 3 such that only a part thereof is under strain whenmovement is induced within the flexible element 3. The piezoresistiveelement 5 a may be part of the flexible element 3. The piezoresistiveelement 5 a may be a layer of the flexible element 3. It will also beclear to one skilled in the art that preferably, saturation of thepiezoresistive element 5 a is not encountered before maximum strain i.e.it has a unique electrical resistance for a unique applied strain (andassociated movement of the flexible element 3)

FIGS. 5 and 6 are perspective views of further embodiments of thecurrent invention, again with flexible element 3 in a ‘pre-stressed’state—initially straight. In these embodiments, detection of themovement of a flexible element 3 is undertaken using optical techniques,replacing the Wheatstone bridge circuits 5 and the variablecapacitance/resistance elements of the aforementioned embodiments. Savefor this replacement, the structure of the body region 2, heater 4 andflexible element 3 is identical to that described in relation to FIGS. 1and 2, thus the functionality of these detection devices 1 remainsunchanged. Hence, elements present in FIGS. 5 and 6 that are present inFIGS. 1 and 2 are given like reference numerals.

Referring to FIG. 5, the detecting device 1 comprises a body region 2, aflexible element 3, a heater 4 and a waveguide structure 9. Thewaveguide structure 9 is located within the detecting device 1,extending from the body region 2, through the flexible element 3 and toan outer surface of the flexible element 3 remote to the body region 2.An electromagnetic radiation source 10 is located within the body region2, so as to irradiate an entrance to the waveguide 9 and causeelectromagnetic radiation to be transmitted therethrough. Thetransmitted electromagnetic radiation will pass through the waveguide 9and will be emitted from both the detecting device 1 and the waveguide 9at the outer surface of the flexible element 3 remote to the body region2. The emitted radiation may be detected by use of a photodiode array11. The resolution of the photodiode array 11 can be tailored to thedesired measurement resolution. For example, the smaller the diodes inthe array 11 (or more densely packed they are) the higher itsresolution, thus allowing a smaller movement in the flexible element 3to be detected.

In use, heat is supplied to the flexible element 3 via the heater 4 (orby the local environment) so as to cause it to bend from its initiallybent configuration towards a straight configuration. The degree to whichthe flexible element 3 bends is proportional to the number ofphotodiodes 11 that are excited and thus the movement of the flexibleelement 3 can be determined.

Referring now to FIG. 6, the detecting device 1 comprises a body region2, a flexible element 3 and a heater 4. The flexible element 3 comprisesa grating 12, the grating 12 being formed by transparent and opaquesections parallel to one another. The grating 12 extends along asubstantial length of the flexible element 3, away from the body region2. A photodiode array 11 is located on one side of the flexible element3, and an electromagnetic radiation source 10 on an opposite side, suchthat electromagnetic radiation may be emitted from the source 10, betransmitted through the transparent sections of the grating 12 and bedetected by the photodiode array 11. Depending on the size of the opaqueand transparent sections (or ‘pitch’ thereof) the detecting device 1 canbe used in one of two ways. The grating 12 may be used as a pure lightfilter, the shadow of the grating 12 falling on the photodiode array 11.Alternatively, the grating 12 can be configured so as to cause incidentradiation to diffract. In diffracting, the electromagnetic radiation mayconstructively and destructively interfere with itself, thereby creatingan interference pattern on the photodiode array 11. Most preferably theelectromagnetic radiation source 10 is chosen so that the radiation itemits does not penetrate the opaque sections of the grating 12 i.e.visible light is most preferable to x-rays.

In use, heat is supplied to the flexible element 3 via the heater 4 (orby the local environment) so as to cause it to bend from its initiallybent configuration towards a straight configuration. In bending, thepitch of the opaque and transparent sections will change. Such a changewill have an effect on the electromagnetic radiation that is transmittedthrough the grating 12 and, depending on how the grating 12 isconfigured, either the shadow of the grating 12 or the interferencepattern on the photodiode array 11 will change. Patterns in maxima andminima of the pattern/shadow can be used to determine the change inpitch of the sections of the grating 12, and this change is proportionalto the movement (curvature) of the flexible element 3.

It will be appreciated that the transmissive grating 12 could bereplaced with a reflective grating 12. The device 1 operates in exactlythe same way, apart from the fact that the sections of the grating 12are reflective and non-reflective, and the photodiode array 11 is on thesame side as the electromagnetic radiation source 10, thereby detectingreflected, as opposed to transmitted electromagnetic radiation.

For all embodiments utilising optical detection methods, it will beappreciated that preferably the radiation source 10 and photodiode array11 are chosen so as to compliment one another. For example,electromagnetic radiation from a source 10 with a peak emissionwavelength of 640 nm (red light) may be best detected with a photodiodearray 11 with peak sensitivity either at or near that wavelength.Furthermore, it will be appreciated that the photodiode array 11 can beone or two-dimensional. A two-dimensional photodiode array 11 can beused to image the transmitted/reflected electromagnetic radiation. Forexample, in the case of the embodiment comprising a grating 12, theentire fringe pattern may be detected with a two-dimensional array 11,whereas a one-dimensional array 11 will only yield information in a lineacross said fringe pattern. Although a one-dimensional analysis may besufficient, the detection and capturing of a two-dimensional image maybe of some use. It will be obvious to one skilled in the art that thephotodiode array 11 may be replaced with any detecting element with thedesired properties in terms of detection range, resolution etc. Forexample, the detection of electromagnetic radiation may involve opticalfibres and associated processing means.

It will be obvious to one skilled in the art that all of theaforementioned embodiments are not restrictive in any way, and are givenby way of example only. It will be clear that various modifications maybe made to the detecting device 1 while not detracting from theinvention.

For example, although the determination of fluid properties has beenshown to incorporate the use of the flexible element 3 moving from aflat to curved position, or curved to flat position, other ‘initial’ and‘final’ positions or ‘configurations’ of the flexible element arepossible. The flexible element may move from a first curvedconfiguration to a second curved configuration. In order to determineproperties of a fluid, the flexible element must move from a firstconfiguration to a second configuration. It may also move to otherconfigurations thereafter. The first and second configurations may bethe same.

Latching means may be provided to hold or ‘latch’ the flexible element 3in a desired position. For example, if the flexible element 3 comprisesa magnetic material (such as cobalt) an electromagnet located adjacentthe device 1 can be used to latch the flexible element 3 in a desiredposition. Alternatively, a magnetic material may be fixedly attached tothe flexible element. When the electromagnet is ‘on’ it may be arrangedto attract the magnetic material and consequently the flexible element3. Alternatively, it may be arranged to repel the electromagnet.

Whether the electromagnet generates an attractive or repellent force, ifthe flexible element 3 is resilient, a build up of potential energy inthe flexible element 3 (due to elasticity of the element 3) may opposethe attractive or repelling magnetic force. Such a build up of energycan generate a restoring force that may attempt to restore the positionof the flexible element 3 to its equilibrium position. If the magneticforce is such that it counterbalances the restoring force, the flexibleelement will be ‘latched’ in a desired position.

The electromagnet may be integral to the device or the electromagnet maybe a separate piece of apparatus. Alternatively, the flexible elementmay comprise an electromagnet, and the magnetic material may be aseparate piece of apparatus. It will be appreciated that anycontrollable source of variable magnetic field may be used instead of anelectromagnet.

In an alternative embodiment illustrated in FIG. 7, the flexible element3 forms one plate of a capacitor like structure. The flexible element 3comprises an electrically conductive layer 3 c (such as gold) forming afirst plate of the capacitor like structure. Another electricallyconductive plate 13 (such as gold) forms a second plate of the capacitorlike structure, and is located on the body region 2 of the device 1.

A potential difference applied between these two plates 3 c, 13 causesopposing charges to build up on each plate 3 c, 13, and an electricfield is established between the plates. As opposite electrical chargesattract, the plates 3 c, 13 will be attracted toward each other. It willbe appreciated that this attractive force (electrostatic force) can beused to hold or latch the flexible element 3 in a desired position.Preferably the second plate 3 c is fixed in position, i.e. not free tomove, to ensure that when latched, the flexible element does not move asa consequence of any movement of the second plate 3 c.

If the flexible element 3 is resilient, a build up of potential energyin the flexible element 3 (due to elasticity of the element 3) mayoppose the attractive electrostatic force. Such a build up of energy cangenerate a restoring force that may attempt to restore the position ofthe flexible element 3 to its equilibrium position. If the electrostaticforce is such that it counterbalances the restoring force, the flexibleelement will be ‘latched’ in a desired position.

Electrical contact between the plates 3 c, 13 is undesirable. The device1 can be structured such that such electrical contact is not possible.For instance, the second plate 3 c may reside in a recess in the bodyregion 2 such that, even when the flexible element 3 is flat, the first3 c and second plates 13 are spatially separated and electrical contacttherebetween prevented. Alternatively, in some embodiments, one (oreach) of the plates is (are) coated in an electrically insulative layer(not shown) to prevent such electrical contact. The electrical insulatormay be a plastic material.

It will be appreciated that the second plate 13 may not reside on thebody region 2. For example, the location of the second plate 13 needonly be such that an electric field may be established between theplates that is sufficient in magnitude to latch the flexible element 3in a desired position.

Latching of the flexible element 3 has significant advantages. Forexample, the flexible element 3 is formed of (at least) two layershaving different coefficients of thermal expansion. When heated, theflexible element 3 moves from a first configuration to a secondconfiguration. An electric or magnetic field can then be applied to holdthat flexible element 3 in position, whereafter the heat can be removed.The temperature of the flexible element 3 can then return to the ambienttemperature of its surroundings i.e. the fluid in which it is immersed.The flexible element will then be resiliently biased to return to thefirst configuration. The electric or magnetic field can then be removed,allowing the restoring force due to the temperature change to move theflexible element 3, and the motion of the flexible element 3 to becharacterised at this ambient temperature. Thus, the heat required tomove the flexible element 3 does not affect the results of theexperiment. Furthermore, the use of electric or magnetic fields to holdthe flexible element 3 in position is more energy efficient than the useof heat (or current supplied to a heater), thus reducing the powerconsumption of a device incorporating such features.

As hereinbefore described, it will be appreciated that the capacitorlike structure may also act as a variable capacitor. By applying aconstant potential difference between the plates 3 c, 13, the separationbetween the plates 3 c, 13 can be extrapolated from the capacitance ofthe capacitor using simple electrostatic theory. If the separation ofthe plates 3 c, 13 changes, so will the capacitance of the capacitor.Thus, as the flexible element 3 comprises one plate of the capacitor,the variable capacitor can be used to detect and characterise movementof the flexible element 3.

Furthermore, the flexible element 3 may not be a laminate of twomaterials. The flexible element 3 may comprise more than two materialsand/or layers e.g. it can be formed of multiple layers of piezoresistivematerial, or any other desired material. It will be appreciated that theflexible element need only be capable of moving from a first to a secondconfiguration when heated. Preferentially the movement is relativelylarge. This can be achieved by selecting materials with appropriateproperties (such as certain Young's Modulus' and Coefficients of ThermalExpansion), such that a small applied heat signal generates a relativelylarge movement of the flexible element 3. This is preferentiallyachieved by the use of a laminate of two or more layers. One layers cancomprise a polymer. One layer can comprise a metal. The polymer may be apolyimide, polyamide or acrylic polymer. The metal may be aluminium orgold. The relatively large movement may facilitate the use of movementdetectors incorporating optical methods and/or apparatus.

It will be appreciated that the size of the detecting device 1 may bechosen to suit a specific application to the situation. It will beappreciated that the size of the flexible element 3 may be chosen tosuit a particular application. For example, sizes may range from theorder to micrometers to the order of millimetres e.g. 1 μm to 10 mm. Thelength of the flexible element, defined as the distance from the firstto the second end, may be, for example, 100 μm to 1 mm. The shape of theflexible element 3 is also variable. For example, the flexible element 3may taper away from the body region 2. The flexible element 3 may flareoutwards and away from the body region 2. The flexible element 3 may notbe one continuous object. For example, the flexible element 3 may be athin rectangular layer with sections cut out thereof. This may be forhydrodynamic purposes or otherwise. The flexible element 3 may evencomprise an additional element secured to an end remote to the bodyregion 2, for example a paddle. The paddle may be integral to theflexible element 3. The inclusion of a paddle may be used to increasethe surface area of the flexible element, which may, for example,increase the detection sensitivity of the device for flow and shear ratemeasurements.

The heater and movement detector element may be separate. Alternatively,the heater 4 and movement detector element may be combined such that asingle element performs both of the functions thereof. If the heater 4comprises a material that is piezoresistive, the heater 4 may alsofunction as the piezoresistive element 5 a of the movement detector. Thecombined heater-movement detector may comprise a single material, suchas gold. The piezoresistive behaviour of gold may be greatly enhanced bythe use of an elastic support layer, such as a polyimide layer.

In order to form such a combined multi-layer heater-movement flexibledetector element, a polyimide track is deposited on the flexible element3, followed by a gold layer on top of that track. It will be appreciatedthat many configurations are possible in order to realise a combinedheater-movement detector element. In order to function, theheater-movement detector element must dissipate heat and exhibitpiezoresistive behaviour.

The flexible element 3 can be constructed so as to be straight atequilibrium (no applied signal) using specific fabrication methods. Forexample, specific stresses may be induced in one or more layers duringheated fabrication thereof.

The type, shape and location of heater 4 may be chosen to suit thesituation or design criteria. For example, the heater 4 may be on thetop surface of the flexible element 3. The heater 4 may be located onthe underside of the flexible element 3. The heater 4 may be embeddedwithin the flexible element 3. For example, the heater 4 may residebetween layers if the flexible element 3 is a laminate structure. Thismay ensure that the majority of heat is dissipated in the flexibleelement 3, as opposed to a fluid sample. This has two advantages, namelythat efficiency is increased and, more importantly, the temperature ofthe sample is not raised artificially and thereby adversely affectingmeasurement. The heater 4 may be an electrically conductive materialthat dissipates heat. The heater 4 may be a separate device such as anon-integrated electrically conducting filament. The heater 4 may be athin-film deposition of an electrical conductive material. The heater 4may be a track of a conductive material. For example, the heater 4 maybe an electrically conductive track that weaves along, and back andforth across the flexible element 3, thereby creating a uniformdissipation of heat thereon.

Cooling elements can also be employed on the flexible element 3. Byincorporating coolers, the flexible element 3 could be made to bendusing differential expansion of constituent layers of a laminar flexibleelement 3 if those layers possessed different coefficients of thermalexpansion. The direction of movement would be opposite to that when heatis applied to the flexible element 3.

The detecting device 1 may also comprise a combined heater and coolerfor heating/cooling of the fluid itself, such that measurements may bemade at selected temperatures. This heater and cooler may reside on thebody region 2 or on the flexible element 3. A movement (e.g. current)signal applied to the heater 4 may be any predetermined function. Forexample, the signal may be a sine wave, a modulated sine wave, a squarewave, a single pulse or a continuous current of a constant value.

It will be clear that by using a plurality of flexible elements 3simultaneously, a plurality of measurements can be simultaneously made.For example, using three independent flexible elements 3, thetemperature, viscosity and flow rate of a fluid sample can be measuredsimultaneously. A plurality of devices 1 may be used in order to obtainthe desired number of flexible elements 3, each device comprising one ormore flexible element 3. Alternatively, a single device 1 comprising thedesired number of flexible elements 3 (appropriately configured) may beused. The flexible elements 3 may be in any desired configuration. Forexample, two rows of the flexible elements 3 may be interdigitated.

A spatial profile of the properties of a fluid can be obtained by usinga plurality of flexible elements 3/devices 1 located at differentpositions within the fluid. Thus, by using a device 1 comprising aplurality of flexible elements 3, such a profile can be readilyobtained. It will be appreciated that such a profile can be obtained inreal-time. For example, by measuring the flow rate of a fluid at aplurality of locations, the shear rate of the fluid may be obtained. Byobtaining profiles in real-time, changes therein can be accuratelydetermined. Such changes may be natural, for example the loss of heatenergy, or induced, for example the introduction of a chemical to thefluid.

It will be appreciated that, just as a fluid can have an influence on aflexible element 3, a flexible element 3 may have an influence on thefluid. For example, movement of a flexible element 3 in a fluid maycause turbulence therewithin. Movement of a flexible element 3 in afluid may also cause flow therewithin. Co-ordinated and specificmovement of a plurality of flexible elements 3 can cause a specific flowin the fluid. Thus, flow can be artificially induced in a fluid. Forexample, flow can be induced in a fluid in order to simulate the flow ofthat fluid in a pipe. Properties of the fluid may then be determinedwhile the fluid is undergoing such flow.

Using a plurality of flexible elements 3, some of the plurality maycause flow within a fluid e.g. by cyclically operating the elements 3.One or more other elements 3 may be used to characterise that flow. Forexample, a device may comprise seven flexible elements 3 arranged intotwo rows. The first row may comprise a first, third, fifth and seventhflexible element 3, and the second row a second, fourth and sixthflexible element. The flexible elements of the first row may extend in afirst direction. The flexible elements of the second row may extendgenerally in a direction parallel but opposite to the first direction.Thus, the flexible elements of the first row are in opposition to thoseof the second row. In this embodiment, the seven flexible elements areinterdigitated. The first, third, fifth and seventh flexible element 3may be arranged to generate a flow within a fluid.

For example, movement of the first, third, fifth and seventh flexibleelement 3 can be controlled such that the movements ‘cascade’. As thefirst element is made to move from the first to the secondconfiguration, the third element 3 is made to move from the second tothe first configuration, and as the third element 3 is made to move fromthe first to the second configuration, the fifth element 3 is made tomove from the second to the first configuration etc. While the first,third, fifth and seventh flexible elements generate flow in the fluid,the second, fourth and sixth elements can be used to characterise thatflow. For example, they can be used simultaneously to determine theshear rate of the fluid. Alternatively, or additionally, they can beused to determine different properties. For example, the second flexibleelement 3 may determine temperature of the fluid, the fourth flexibleelement 3 the fluid viscosity, and the flow rate may be determined bythe sixth flexible element.

The device 1 may reside in a container such that environmentalconditions within the container may be accurately monitored andcontrolled. For example, pressure and/or temperature within thecontainer may be monitored and/or controlled. Such monitoring may beimplemented and control exerted upon on any fluid residing within thecontainer. It will be appreciated that only the flexible element(s) 3 ofthe device 1 may reside within the container, with the body region 2 ofthe (or each) device 1 residing outside of the container. Control orknowledge of the temperature of the fluid is useful when the viscosityof the fluid is being measured. This is especially true in themeasurement of blood viscosity, as the viscosity of blood variessignificantly with changes in temperature. Thus, temperature controllingand sensing devices may be used to actively control the temperature ofthe fluid within the container. For example, heaters and/or coolers maybe used. The heaters and/or coolers may be independent apparatus,completely separate from the sensing device 1. Alternatively, theheaters and/or coolers may be integral to the sensing device 1. Thetemperature sensing device may also be separate from or integral to thesensing device 1. It will be readily appreciated that the temperaturesensing device may be a flexible element 3 comprising layers of materialwith different coefficients of thermal expansion, as hereinbeforedescribed.

It will be appreciated that the detecting device 1 may form an integralpart of a larger, more complex system. For example, due to its ease ofmanufacture, the detecting device 1 can be fabricated at a low cost,which introduces the possibility of a readily disposable device 1.Although when determining properties of, for example, water the device 1may or not need to be reusable, it is ideal in some circumstances thatthe device 1 is disposed of after a single use. This may be the case fora number of reasons, for example hygiene, contamination etc. A scenariowhere hygiene and contamination are of critical importance is the areaof blood testing, and in particular the testing of human blood. Thisdevice 1 can be fabricated in extremely small sizes and thus it can beeasily integrated into a blood extraction and testing system.Furthermore, due to the small size, a correspondingly small fluid sampleis required.

For example, blood viscosity is related to deep vein thrombosis whichhas in turn been related to long-haul aeroplane flights. Ideally, apassenger could measure the viscosity of his/her own blood and thereforedetermine whether any blood-thinning agent needed to be taken (e.g.aspirin). The device 1 (or more than once device 1) could be integratedwith a microneedle (for painless extraction of blood), and have readilydetachable electrical connections that are designed to engage likeconnections on a small, handheld processing terminal. A needle anddevice 1 could be attached and thereby electrically connected to theterminal, and the passenger could painlessly extract blood fromhis/herself. Controlled by the terminal, the device 1 would then operateas described hereinabove, and yield information about the blood. Theterminal could include a simple display with information such as theviscosity of the blood, whether it was at a dangerous level etc. Beingsmall and cheap, the needle and device 1 could then be disposed of withlittle cost. The terminal could be used again with another needle anddevice 1. Hence, many devices 1 may be used on a single flight.

It is clear that the functionality of the device 1, together with itssmall size and low cost of fabrication make its use advantageous in awide variety of applications where the determination of fluidproperties, for example viscosity, temperature, flow rate and shearrate, is required. Preferably the fluid is a liquid. Preferably theliquid is blood or a constituent part thereof, such as plasma.Preferably the volume of fluid from which its properties are determinedis of the order of 1 microlitre.

1. A method of determining a property of a fluid using a sensing elementcomprising: providing a flexible element movable from a firstconfiguration to a second configuration via bending of said flexibleelement, said flexible element comprising an actuating portion arrangedto move said flexible element between said first configuration and saidsecond configuration; inducing movement in said flexible element betweensaid first configuration and said second configuration by applying aheat signal to said flexible element; receiving a signal from saidsensing element, said signal being indicative of the induced movement ofthe flexible element within said fluid; and processing said signal todetermine a value indicative of at least one property of said fluid. 2.A method as claimed in claim 1, wherein said actuating portion of saidflexible element comprises a laminate of at least two layers, each layerhaving a different coefficient of thermal expansion, and wherein, priorto induction of movement by application of the heat signal, a valueindicative of the temperature of the fluid is determined.
 3. A method asclaimed in claim 1, wherein the device comprises a plurality of flexibleelements, such that the plurality of flexible elements may be used todetermine a value indicative of at least one property of said fluid in aplurality of locations.
 4. A method as claimed in claim 1, wherein thedevice comprises a plurality of flexible elements, at least one of theplurality being used to cause a flow within the fluid, and at least oneof the plurality being used to determine a value indicative of at leastone property of said fluid.
 5. A method as claimed in claim 1, furthercomprising holding the flexible element in at least one of said twoconfigurations by a magnetic force.
 6. A method as claimed in claim 1,further comprising holding the flexible element in at least one of saidtwo configurations by an electrostatic force.
 7. A method as claimed inclaim 1, wherein said received signal is indicative of a maximumdeflection of the flexible element, said signal being processed todetermine the viscosity of the fluid.
 8. A method as claimed in claim 1,wherein said signal is processed to determine a value indicative of atleast one property of a group comprising viscosity, temperature, flowrate and shear rate.
 9. A method as claimed in claim 8, furthercomprising: determining a rate of change of movement of said flexibleelement, by monitoring a change in the received signal with time; anddetermining a value indicative of the viscosity of said fluid from saidrate of change of movement.
 10. A method as claimed in claim 8, furthercomprising: determining an amplitude of movement of said flexibleelement from said received signal for a given applied heat signal; anddetermining a value indicative of the viscosity of said fluid from saidamplitude.
 11. A method as claimed in claim 8, further comprising:determining a change in said movement of said flexible element; anddetermining a value indicative of a flow rate of the fluid from saidchange in movement, said change in movement being due to flow of thefluid against said flexible element.
 12. A method as claimed in claim11, further comprising: determining a value indicative of a shear rateof said fluid by determination of the flow rate at a plurality oflocations within said fluid.
 13. A device for detecting a property of afluid comprising: a body region; a flexible element having a first endand a second end, said first end being fixedly located on said bodyregion, said flexible element being arranged to move from at least afirst configuration to a second configuration via bending of saidflexible element; said flexible element comprising a laminate of atleast two layers and an actuating portion arranged to move said flexibleelement between said first configuration and said second configuration,the actuating portion being provided by at least a first layer of saidlaminate having a different coefficient of thermal expansion from asecond layer of said laminate such that a change in temperature of saidflexible element moves the flexible element from said firstconfiguration to said second configuration; said flexible elementfurther comprising a heating element for heating at least said flexibleelement thereby providing said change in temperature; and a movementdetector arranged to detect said movement of said flexible element, andto provide a signal indicative of a property of a fluid in which theflexible element is immersed.
 14. A device as claimed in claim 13,further comprising latching means arranged to hold the flexible elementin at least one of said two configurations.
 15. A device as claimed inclaim 13, wherein said movement detector comprises an electromagneticradiation source arranged to direct radiation towards said element, andan electromagnetic radiation detector arranged to detect electromagneticradiation at least one of: reflected from, transmitted through,refracted from or diffracted by said flexible element.
 16. A device asclaimed in claim 13, wherein the length of the flexible element from thefirst end to the second end is between 100 μm and 1 mm, and wherein thedistance between the second end of the flexible element in said firstconfiguration and the second end of the flexible element in said secondconfiguration is between 30 μm and 650 μm.
 17. A device as claimed inclaim 13, wherein at least one of the first and second layers of saidlaminate comprises a polymer.
 18. A device as claimed in claim 17,wherein at least one of the first and second layers of said laminatecomprises a material selected from a group consisting of polyimides,polyamides and acrylic polymers.
 19. A device as claimed in claim 13,wherein the second layer of said laminate comprises a metal.
 20. Adevice as claimed in claim 19, wherein the metal is selected from agroup consisting of gold or aluminium.
 21. A device as claimed in claim13, wherein the device comprises a plurality of flexible elements.
 22. Adevice as claimed in claim 21, wherein the plurality of flexibleelements are arranged in a first row and a second row, each rowcomprising at least one flexible element, the flexible elements beingarranged such that the at least one flexible element of the first rowextends in opposition to the at least one flexible element of the secondrow.
 23. A device as claimed in claim 22, wherein the plurality offlexible elements are interdigitated.
 24. A device as claimed in claim13, wherein said movement detector comprises a piezoresistive elementlocated on said flexible element arranged such that the electricalresistance of the piezoresistive element changes due to movement of saidflexible element.
 25. A device as claimed in claim 24, wherein saidpiezoresistive element is located on the flexible element at a positionremote from the body region.
 26. A device as claimed in claim 24,wherein said piezoresistive element is formed as a layer of the laminateof said flexible element.